Thermionic vacuum tube and circuit



Aug 22, 1950 R. H. VARlAN 'THERMIONIC VACUUM TUBE AND CIRCUIT Origixial Filed March 8, 1939 5 Sheets-Sheet l FIGZA INVENTOR. RUSSELL H. VARIAN fl M ATTORNEY Aug. 22, 1950 R. H. VARIAN 2,519,420

Tl-IERMIONIC VACUUM TUBE AND CIRCUIT Original Filed March 8, 1939 5 Sheets-Sheet 3 FIELD INVENTOR. RUSSELL H. VARIAN ATTORNEY Aug. 22, 1950 R. H. VARIAN THERMIONIC VACUUM TUBE AND CIRCUIT 5 Sheets-Sheet 4 Original Filed March 8, 1939 INVENTOR. RUSSELL H. VAR IAN ATTORNEY A g- 1950 I R. H. VARIAN THERMIONIC VACUUM TUBE AND CIRCUIT 5 Sheets-Sheet 5 Original Filed March a, 1939 FIG. u

n 14 v +IHL .W H 7 m M" Z, M m w. WAI A I a 5/ M. 3+ \w W ng INVENTOR m w. v M H. m L6 L, E S S U R The phenomenon of active grid loss which is overcome by the present invention may be explained in connection with the conventional three-electrode tube of Fig. 1. In this figure there is shown an electron emitting filament I, a control grid 2, and a plate 3 or anode in an evacuated container 4. The filament I is heated by a battery 5; the grid 2 is biased by a battery 6, and the plate 3 is energized by a battery "I. A resonant circuit 8 comprising a condenser 9 and an inductance I 0 impresses an alternating difference of potential on the grid 2. An inductance H in series with the plate circuit is inductively coupled to inductance III for feedback control. A resistor I2 represents the load to which the system delivers energy, and an inductance I3 connected to a generator I4 and inductively coupled to inductance I0 represents the source of alternating current excitation for the system. The system as shown is capable of operating as an oscillator, as an amplifier or as a detector depending on factors of design and adjustment. The general theory of operation is well known in the prior art and will in the following be assumed without explanation except in so far as the effect of active grid loss is concerned.

In the operation of the tube of Fig. l at low frequencies the time required for an electron to travel from the filament I to the plate 3 is small compared with the period, that is to the time interval corresponding to a cycle of operation. The grid 2 has its potential varied with respect to the filament I potential at the frequency of the system, and the impedance of the space between filament I and plate 3 is varied in accordance with the potential during the time the electron is passing from filament I to plate 3. Under these conditions energy is not transferred between the grid 2 and the electrons which pass through the grid. This statement should not be confused with the fact that a positively charged grid carries current. To avoid possible confusion, however, the subject of grid loss will be explained with reference to a grid which is negative with respect to the filament at all times, and thus does not collect electrons from the surrounding space.

It is well known in the art that so long as grid 2 remains at a constant potential, it may control the number of electrons passing from electron emitter I to plate 3, but it cannot influence the energy with which electrons strike plate 3. This follows because whatever the potential of grid 2 may be, the electrons in passing the grid are merely passing a potential valley or hill as the case may be, and the energy lost by the electrons in ascending the hill is all regained in going down the other side. If the grid represents a potential valley, the same is true with the signs reversed. The same is true also if the potential of the grid is changing slowly, and it is easily seen that it will remain true as long as the grid does not change its potential appreciably while the electron is in transit between filament I and plate 3.

If on the other hand the grid 2 does appreciably change its potential while an electron is in transit between filament I and plate 3, the electron may strike the plate with either increased or diminished energy, for if the height of the potential hill, or the depth of the potential valley, at grid 2 changes while the electron is in transit, the energy lost on the ascent side will in general not equal the energy gained on '7 4 the descent side. The matter of whether the depends on the phase of the change when the electron passed through the field of grid 2.

If a stream of electrons uniformly distributed in time crosses the cyclically varying potential hill or valley at grid 2 there will be as many electrons gaining energy as losing energy, and if the gain or loss is small compared with total energy, the cyclic variations in the barrier, that is, the potential of grid 2 will not increase or decrease the average energy with which the electrons strike the plate 3. However, in a threeelectrode tube the electron stream is not uniformly distributed in time, and it therefore becomes necessary to investigate the phase relations existing between the maximum electron emission and the grid potentials to determine whether the electron stream on an average gains energy from, or loses energy to, the grid circuit. The greatest number of electrons will leave the filament I when the grid 2 is most positive, and

these electrons will gain energy from the grid circuit in traveling from the filament I to the grid 2, and since the grid 2 will be more negative while the electrons complete their journey from the grid 2 to the plate 3, these electrons will not lose the energy they gained in traveling from the filament I to the grid 2. Hence, the grid 2 will lose energy to the electron stream. This is known as active grid loss.

With the tube shown in Fig. 1 operating at high frequencies, the time required for an electron to travel from the filament I to the plate 3 may become comparable with a period of oscillation of the system. In tubes of ordinary dimensions, the transit time in the tube becomes comparable with the period at frequencies of the order of III cycles per second or less, the larger the tube in general the lower the frequency where transit time becomes appreciable. When the transit time of the electron traveling from filament I to plate 3 is an appreciable fraction of the oscillation period, the potential of grid 2 with respect to filament I changes materially during the time of transit of the electron from the filament I to plate 3, and the tube is thus subject to active grid loss.

The active grid loss is understood in the prior art. Some attempts to overcome this loss have been made, and in particular attempts to reduce the transit time of electrons in the tube by reducing the spacing between the electrodes, but none of the attempts known prior to Patent No. 2,244,747, issued June 10, 1941, in the names of Russell H. Varian and Arnold J. Siegert, and to the present invention, did more than reduce the effect by dimensional design.

In the present invention, as in the above-mentioned patent, the factors which determine active grid loss are controlled in such a way that the active grid loss may be eliminated entirely or reversed in sign so that the control grid may be caused to gain energy from the electron stream instead of imparting energy thereto. The methods whereby these results are accomplished in the present invention are somewhat simpler and more easily carried out in practice than those described in the specification above referred to.

As has been shown in the foregoing analysis of active grid loss, when a three-electrode tube, having conventional spacings, is connected in the ordinary way and operated at high frequency, there will be an active grid loss. This does not,

however, :apply to all possible element .-.spacings and connections of a three-.electrcdeztube. One such -exception is shown in :Eig, 2. .In .the opera tion of the three-electrode tube shown ii-n :Fig. :2,

a radical departure is made fromconventional practice, namely, in that .insteadzof-the. anode and grid potentials being in opposite ;phase with respectto-eachother, these potentials are approximately in the same phase. .It w-ill now be shown qualitatively that energy will be delivered to a. resonant-.oircuit'by a stream of-electronspassingbetween cathode and anode.

Two resonant circuits-are shownin Fig. 2=which circuits consist of respective resonators formed bya concentricpair of concentric-lines,the inner pair-consisting of cathode l and;grid 2' having closely spaced conducting grid wires and a con-- ducting top ;plate 2, and conductorsv'3'1and 41, whichgare electrical 'cont-inuations of cathode and ;grid 2". The second consists oirgrid 2"":and electron-permeable anode 5' also :having .a .conducting top plate "5" and conductors 4" and which are electrical continuations .of gridZ and anode t5. respectively. A coupling conductor :1" linksgsome of th 'fie'ldfin both resonators, and serves :to couple the two resonant circuits together, alfrSllCh couplingrissdesired in a. particular case. .An; annular member -8 is employed for closing the end of the outer :concentriclineand for-.tuningt-he sameioy sliding this annularmemberinaandout. It consists of "two metal plates separated by a thin layer of insulating material. which makes it possible .to maintain conductors d'randxfi' at diffierent direct current potentials and-at the same time provides a free path 'for passage .of' high frequency currents between "the twouconductors. A similar annular member 9' serves thesametpurposes for'the'inner concentric line. Asradiating dipole'lfi' (seeiZFig. 2A) 'may'be connectediby a concentric line to the'outer of the concentric line resonators for linking the flux therein asbyaloop at lil! for removing energy therefrom. .A- dipole i 2 is connectedto the innerresonator by concentric line [3' for delivering energy thereto. The twoclipoles ifiandm' are notzintended to be used simultaneously, .butare shown as alternative :arrangements, Ill! being used 'if the device is serving as a transmitter,

and 12 -be ng used if the device is serving as -'areceiver. Ifthe device-is used 'asa receiver, the cylindrical plate 14' maybe used as a detector andsthe rdetected signal is. removed through a wire bereplaced by abiasing battery or other source of potential. If the spacing between cathode I andagrid- 2," and the potential tgradientbetween cathode l-and grid 22. isrsuch that an electron leaving :cathode l takes approximately one-half cycle to travel from cathode/i Eto grid 2', the

electronstream as a whole 'will do work .on the grid 2 as is shownin Fig.3;

In -Fig-.'-3 positive values of-thesine curve representgradients between cathode l and :gridi" which .tend to accelerate electrons traveling between cathode 1 electrons traveling between :cathode zl :and grid 2''.; The greatest electron current will leave cathode l approximately. when .grid :2 is most and :grid .2" while negative values represent'gradients tending to dec'eleratepositive, :or rat: the timer markediTlln. Due :to the.

presenceof the space. chargeeharrier at .thescathode and 'to the fact that'electrons leaving the; cathode have initially only their thermal velocities, actually-the greatest number of electrons will leave the virtual cathode slightly ins-front of the cathode -l at the time the grid ismost posi-' tive. This involves -.a correction which .may ap preciably shift the phase :of the electron groups "at very high frequencies, but at frequencies of the order of 3 I0 cycles and lower it may be.

neglected. This greatestxelectron cur-rent will do work on the grid if it remainsin transit between cathode land grid 2" for the'time interval Tz-To,

as shown-in Fig. -3. This allows t'hese electrons.

to be'accelerated for a quarter cycle and decelerated for a quarter-cycle.

According to the convention adopted in this figure, the shaded-area above the axis represents velocity gained from the-'gridcircu-it by'this-most numerous group of: electrons that leavesthe-cathode when most negative'during thefirstquarterof a cycle, while the shaded area below the axis represents the velocity lost-by theelectrons in the next ensuing quarter-cycle.

This isso because the-curve isa 'graphical rep resentation of the force acting on theelectrons as -'a function of time, and

. Velocity=kf ,fdt

where f=f0rce and t=time. Since the area-:blow' the axis is as greatasthe=areaabove, theseelectrons lose-asmuch velocity as-they gain intraveling from cathode l to gridZ".

The energy gained'or lost by the electrons in traveling from cathode l-to-grid'Z is where Die the distance. Since the electrons are continuously gaining velocity from the direct cur rent field intheir flight from the cathodeto grid 2", the electrons travel farther per unit time in the'last half-0f their night than they did'in tl're first half, and hencethere is a preponderance of energy lost over energy-gained by the electrons.

In Fig. 4 the velocity-changes are shown for electrons outof phase-with those-shown -in Fig. 3. It can'beiseen that this-group of electrons-- gains as much velocity per electron fromthegr'id.

circuit as was lost per electron by the=previous:and-

larger group of electrons but since this isthe least numerous group of electrons, they will not eXtract-as'much energy from the grid'circuitas themost numerousgroup of electrons addedltoit.

Following the same-procedure we-may take any other group of electrons as forinstance the-one leavingcatho'ole'l at time T3 and arriving at grid 2"at time T4. This group'of electrons loses more energy per electron than the group leaving at T0, but there is a corresponding .zgroup leaving cathode hat time T3, Fig. -4, and arriving-at grid 2" at the time T4 which gains asmuch energy per electron from the grid circuit as the-other group lost to it, both; willbe noticedthat'the first mentioned group leftthe-cathode whenthe grid was more positive than its means value whereas :the second group left the cathodeawhen the;;.grid was less positive than :its mean value, and hence the first group will be more numerous than the second' .group and the combined effeot of both-.agrollpg will be to -give up energy to the grid circuit. Similarly, other corresponding pairs j of electron groups may be chosen till the whole cycle is covered, and it will be found that over much the greater part of the cycle the electron groups that deliver a given energy per electron to the grid circuit contain more electrons than the corresponding group that extracts the same energy per electron from the grid circuit. Of course the limited region in Figs. 3 and 4 in which the electrons that gain energy from the grid are more numerous than those that lose the same amount of energy to the grid represents an actual loss of energy by the grid circuit. However, the amount of energy loss is proportional to the amount of energy lost per electron of the energy losing group, multiplied by the difference between the number of electrons in the energy losing group and the number in the energy gaining group, and by inspecting the diagrams it may be seen that this product is rather small and hence does not detract from the energy gained by the grid circuit over the entire cycle.

This is valid proof that the electron stream as a whole will deliver energy to the grid circuit, and hence the so-called active grid loss under these conditions will be negative in sign. This analysis does not, however, prove that the flight time above considered of the electrons passing from cathode to grid given the maximum gain of energy from the electrons, and as a matter of fact it does not. However it constitutes a usable flight time, and in some cases a desirable one. The active grid gain in this case is not large, but in an amplifier an active grid gain large enough to cancel all other losses, and cause the circuit to oscillate may be desirable.

The largest active grid gain occurs when the flight time of the electrons between cathode and grid is somewhat greater than one-half cycle.

Due to the fact that the group of electrons, having the maximum gain of energy per electron, is not the most numerous group of electrons, and that the velocity of electrons increases from cathode l to grid 2", and is influenced by space charge, an exact analyses is difficult to make. Hence, the foregoing qualitative analysis is given in the belief that it is more understandable than an exact analysis would be if it were made.

This analysis neglects certain factors which should be'noted here; firstly, it neglects the influence of space charge; secondly, it neglects the fact that the tubes shown have cylindrical symmetry, and therefore the field strength increases toward the cathode. The field strength in a space charge field between parallel plates increases approximately as D These two neglected terms have opposite effects, and can be made to approximately cancel each other by choice of suitable ratios for the diameter of the cathode and the control grid. Another neglected factor is the grouping of electrons in the electron stream by the efiect of fast electrons from the cathode tending to catch up on slow electrons that left the cathode at a slightly earlier time.

We will now consider the conditions which must exist between the grid and anode in order that the electron stream may deliver a maximum of energy to a resonant circuit of which the grid and the plate are a part.

Obviously, the greatest energy will be delivered to the grid-anode circuit when the line integral of fdD taken from grid to anode for the average electron has its greatest value, and this can always be made a maximum for a particular gridtO-anode spacing and potential difierence by ad- ,imum active grid gain.

justing the phase relation between the grid-fila- I ment and grid-anode circuit.

In the case just described, the most numerous group of electrons pass the grid when it is most negative with respect to the filament, and hence, if the electron flight time from grid to anode is short compared to a half cycle of the oscillating frequency, the grid-anode circuit should be substantially in phase with the grid-filament circuit, for under these conditions the motion of the most numerous group of electrons will be opposed by the strongest field, and hence retarded the most. If the flight time from grid to anode is an appreciable part of a half cycle, the phase in the grid-anode circuit should be somewhat retarded with respect to the grid-filament circuit, so that the most numerous group of electrons will enter the grid-anode interspace a little before the opposing field has reached its maximum, and will reach the anode a little after it has passed its maximum. Since the electrons are normally gaining velocity from the direct current field in the grid-anode interspace, and as has been said before, the work done on the electrons is the line integral of MD taken from grid to anode, the field should reach its maximum somewhat after the middle of the time interval during which the most numerous group of electrons is passing from grid to anode.

In the above-mentioned previous patent, No. 2,244,747, an arrangement was disclosed in which the electron transit time between cathode and grid was about cycle, and the flight time beween grid and anode was preferably enough to bring the total flight time between cathode and anode to roughly 1 cycles. In that case the alternating fields between cathode and grid, and cathode and anode, were substantially apart in phase. This gives substantially a max- By reference to Fig. 3, it may be seen that a continuous transition from the case described in this specification to the case described in Patent No. 2,244,747 is possible. As the time To-T2 is lengthened, the phase of the grid-anode circuit should be shifted by the same fraction of a cycle that the flight time between cathode and grid is lengthened.

It is therefore apparent that if the flight time between cathode and grid lies between To-Tz and a point beyond ToT5, that is, between one-half period and more than three-quarters period, the active grid loss will be negative, and that for any flight time between or beyond these limits, a proper phasing of the electric field in the anode circuit, with respect to that in the grid circuit, will cause the electron stream to deliver maximum power to the grid-anode circuits.

In Fig. 2, suitable means are shown for obtaining all possible phase differences between the cathode-grid and grid-anode circuit. In this figure the cathode l and the conductor 3' form the inner member of a concentric line resonator, while grid 2 and conducting tube 4' form the outer member of the concentric line resonator. Also, grid 2" and conducting tube 4 form the inner member of a second concentric line resonator, of which anode 5" and conducting tube 6 form the outer member. If the mesh of the grid is fine, as would ordinarily be the case, and no other coupling means is supplied, the two resonators are independent of each other. If a coupling member, such as coupling conductor 1' is inserted between the two resonators any desired degree of coupling may be obtained, and since members 8' and 9' which short the concentric lines fOraIternating current-are adjustable, each concentric line resonator is separately tunable. Asiswell known in-the art, the phase angle between two coupled resonant circuits may be varied: by detuning one resonator slightly with respect te the other.

Ina device such: as'has justbeen described, the energy with which an electron impinges on a conductor has no necessary relation to the potential of theconductor at the instant when the electron impinges. This is because the electric fields'throughwhich the electron passes change markedly while the electron is in transit. Another feature of the d'eviceshown in Fig. 2 is that the alternating electricfields are substantially completely confined within their respective concentric lines, and the electrons passing from the cathode through grid 2" and anode pass completely outof the alternating electric field at electron-permeable anode 5-", and hence the alternatingfield' will produce no further changes in electron velocity. The electrons therefore emerge-from anode 5" with varying velocity, and do not' have these variations canceled in traveling from anode 5" to detector plate l4", as would be the casewith an ordinary permeable electrode excited in the ordinary-way. It is therefore possible, for either of these reasons, to use a form of detector in-the-present invention which is inoperative in the usual type of tubes and circuits.

In Fig. 2, anode 5" functions as efiiciently in extracting energy from the electrons in transit between grid 2" and anode 5 as'though it were an impervious cylinder of metal which stopped all the electrons striking it; hence, if oscillating fields exist in the tube, electrons will emerge into thespacebetween anode 5" and metal cylinder i i with velocities difierent from those which they would have had if there had been no oscillating fields. If the oscillations are'weak, as would be the case if the oscillations were caused by a weak signal picked up by antenna I2, therewill'benearly as-many electrons speeded up as are slowed down, and hence detection of the oscillations is most efiicient when detector plate HE is biased so that the difference in number'of electrons caught by cylinder i l when'there are oscillations present, and the number: caught when there are nooscillations present is a maximum. There are two bias points that will meet these conditions, one'whe'n cylinder M is biased so most, but not all, of the electrons. can strike it, and cne when most but not all of the electrons cannot strike it. Cylinder M may detect either by stopping all the electrons striking it an'dallowing them to" be conducted away by condu'ctcr !5, or by emitting an excess of secondary electrons when struck by primaries. If it is to operate by the first method. it should be made to emit as few secondary electrons as possible as by coating it with carbon, or by any other method of preventingemission of secondary electrons. If it is to operate. by the second method, the more secondary electrons cylinder M can be made to emit the better.

The importance of the. fact just. mentioned that makes no difference in the amount of work done on the field; of the circuit by the electrons in a resonator whether the electrons, after passing through the field, are allowed to strike the wall of the resonator, i. e-. anode 5", or are caused to pass through small apertures in the wall or anode, cannot be over-emphasized, for this fact frees us fromv the. well; known. requirementthat a: controlgrid must benegatively. biased producing an oscillator.

to prevent it from extracting energy from the grid circuit due to an alternating current produced by'electrons striking'thegrid. In the device of Fig. 2, the grid-cathode resonator consists of the space within the concentric line of which cathode I and grid 2" form part of the boundary, and it makes no diiierence whatever to the standing waves Within this space what hecomes'of an electron after it has left the fieldconta'inedin this space. Since this is true, it does not change the losses in the grid-cathode circuit to make grid 2 positive and allow electrons to strike it.

We will now consider the effect produced by grid 2 in removing some of the electrons upon the power delivered" to the grid-anodecircuit of which grid 2" and anode 5 are a part. 'In the first place, it is obvious that if grid 2" is posi tive it will leave fewer electrons to excite the an'odecircuit. If'grid 2" removed all equalp'ercentage of electrons throughout the cycle, the result would be "a proportional reduction in the power delivered to the anode circuit. This would not be at all serious, but as a matter of fact'th'e power reduction in the auode circuit will be less than this, and. in some cases may even be reversed in sign; This is because there is a larger proportion of the electrons removed from the electron stream by grid 2" when this grid is positive with respect to cathode l', and it will-be noted that-electrons passing grid 2" in this phase relation extractenergy from the anode circuit instead of adding energy to' it, and 'hencethe more electrons of this phase relation removed'by the rid the better. Hence, since the direct current conductance of" grid 2" is a measure of the electron current removed by grid 2" over the whole cycle, and the alternating current conductance is a measure of the current removed as-a result of the alternating current potential on grid 2", the removal of' current by grid 2 will benefitthe anode circuit if the alternating current conductance'exceeds the direct current conduct'ance. This is not likely to be true in genera] but the -'alternating current conductance ma be counted on to minimize the loss in power caused. by the direct current conductance of" grid 2".

In Fig. 5 is shown an alternative method of The basic mode of operation is the same as in Fig. 2. In Fig. 5, cathode and grid 2-" are used as in Fig. 2. I8 is a cylinder serving the same purpose as anode 5" in Fig. 2-. In this figure the flight time of electrons-between cathode I and grid 2" is preferably arranged to be about a half-cycle, and the flight time between anode 2- and cylinder I8 is preferably'less than a quarter cycle. An annular inwardly projecting flange 19' is provided on cylinder i8, and serves to form acondenser with an annular ring 20', which is attached to the low ends of the grid wires of grid 2"; Annular ring 2'0 in turn forms a condenser with an annular ring 2 I, which latter ring is attached to-the cathode l. By means of these two condensers, the alternatingcurrent potential is divided so that the potential between cathode 'l and grid 2" i'sa certain fraction of the potential between cathodel and anode cylinder l8; and is substantially phase with it. Cylinder I8 and cathode I and thelower cylinder zzgwmeh is a continuation of cathode l form a resonant concentric line which is closed by member 8 which serves the same purpose as members 8! and:& in Big... 2;. .AlresistorZS: connected'between grid and cathode acts as the grid leak resistance generally used in a conventional oscillator. Resistor 23 is connected to cathode I through a wire 24, and tube 18' is connected to the positive terminal of a battery 25. Cathode I is heated in the usual way by an indirect heater 26 which is energized by a battery I1. Since the phase relations between the various elements of the tube shown in Fig. correspond to those in Fig. 2, it will be clear that the electrons will deliver energy to the'fields in the same way as in Fig. 2. Energy can be removed from the concentric line 22--I8' as by loop ll.

- In Fig. 6 there is shown a somewhat different .type of oscillator which makes use in a novel way of the well known so-called space-charge grid.

In this figure, 1 is the thermionic cathode as before. 21 is a grid which may be omitted if desired. Its function is to limit the electron emission from the cathode, but it does not develop alternating current potentials with respect to the cathode. In the drawing it is shown as electrically connected to the cathode, but in use it may be given any convenient fixed potential with respect to the cathode as by a battery H as shown in Fig. 8. An accelerating grid 28, concentric with grid 21, may be given any desired positive bias by battery 21', and the space current in the tube can be fixed independently of the bias on grid 28 by properly biasing grid 21. Grid 28 is positively biased with respect to cathode I, but in the proper functioning of the tube there is no alternating current potential between 'grid 28 and the cathode l.

. -A grid 29, exterior of and concentric with grid 28, is connected so as to be at substantially cathode potential so that a large part of the electrons passing through grid 28 are brought to rest and repelled back toward this grid. The distance between grids 28 and 28, and the average velocity of the electrons between grids 28 and 29, determine the flight time of the electrons between those grids. The average velocity of the electrons between grids 28 and 29 is determined by the potential difference between cathode I and grid 28. For the best functioning of the oscillator shown in Fig. 6 this flight time between 28 and 29 should be substantially a half-cycle of the resonant frequency of the circuit connecting grids 28 and 29, although a considerable departure from this value is possible.

' The electrons will emerge into the interspace between grids 28 and 29 evenly distributed in time, and since the changes in electron velocity in this space caused by the alternating current field existing in the concentric structure existing between grids 28 and 29 is generally small compared to the average velocity of the electrons, the electrons will remain substantially uniformly distributed in time throughout this space except in the vicinity of the region where electrons are stopped and turned back, and this region is so close to grid 29 that the work done on the electrons from this point to grid 29 may be neglected. Hence, we can say that of the electrons traveling from grid 28 to grid 29, there are as many accelerated as retarded by the alternating current field between grids 28 and 29, and hence the average work done by the alternating current field is negligible. But the electrons which have been accelerated between grids 28 and 29 have a better chance of penetrating beyond grid 29 than the electrons that have been decelerated, and hence there will be fewer of these electrons returning from grid 29 to grid 28 than there are 12 of the electrons that have been decelerated. Therefore, the electons returning from grid 28 to grid 28 will not be uniformly distributed in time.

In Fig. 7, these conditions are illustrated graphically. The electrons that left grid 28 at time T0 are the ones most accelerated, and the area under the sine curve between To and T1 is a measure of the velocity gained by this group of electrons in traversing the distance between grids 28 and 29. The velocity lost by the electrons most decelerated is represented by the area under the sine curve between times T1 and T2. Since there will be fewer of those electrons that left grid 28 at time To returning to grid 28 from grid 29, and more nearly the full number of those electrons that left grid 28 at time T1 returning to grid 28 from grid 29, there is a sinusoidal component of electron current density returning to grid 28 from grid 29. The maximum of this current of electrons will leave grid 29 at approxi mately T2, and they will arrive at grid 28 at time T3, and since grid 29 has been more positive than its mean value during the interval Tz-Tz, the electrons of this group will lose energy to the grid control circuit between grids 28 and 29; moreover, the energy they will lose will be a maximum.

If the electrons passing through grid 29 were merely thrown away, energy would be derived from the electron flow by the circuit of which grid 28 and 29 are a part, and this circuit would with a suitable current break into oscillation. However, the electrons that pass through grid 29 are not thrown away, but are caused to do further useful work.

This will be apparent when the operations of an electron-permeable anode 30 exterior of grid 29 is understood. As is shown in Fig. 6, the concentric line resonator consisting of grids 28 and 29 and the conducting tubes 28 and 29 connecting them is independent as far as currents of its resonant frequency are concerned from the adjoining concentric line resonator consisting of grid 29 and anode 30, and the conducting tubes 29' and 3!! connecting them. Hence, if an alternating current of the frequency of the last mentioned resonator flows from grid 29 to anode 38, oscillations will spontaneously develop in the resonator of such phase as to extract a maximum of energy from the alternating current flowing from grid 29 and anode 38. If the tube in Fig. 6 is operated in this way, it is equivalent to an oscillator operating a power amplifier which is electron coupled to the oscillator. If desired, a coupling may beinserted between the two concentric line resonators as is also shown in Fig. 2. This may be required if it is desired to produce oscillations with a current smaller than that necessary to cause the circuit of which grids 28 and 29 are a part to oscillate without help. If the device shown in Fig. 6 is used as an oscillator, the energy may be radiated by antenna ID, as shown in Fig. 6A, exactly as in the case of the device of Fig. 2A. If it is to be used as a receiver, the signal may be received on antenna l 2'. It is not intended that the receiving and transmitting antenna be used on the same device.

If the device is used as a receiver, it may be used either as a regenerative detector or as an oscillator detector. It is probably more sensitive as an oscillator detector. The circuit consisting of grids 28 and 29 and the connecting conductors is allowed to oscillate, and a signal of a slightly different frequency is introduced from antenna grids.

1 2 The 'beats ibetweenilthese 'etwo frequencies cause' the amplitude 'cfioscilla'tionz te periodically vary; and this periodically varyingcscillation F :wilr be amplified in :the2=resonator= -consisting of *1 grid 29: and anode: 3n andltheir: connecting-iconductorsl The electrons after lo'sing energ'y te the aforementioned res'ona'nt circuit arm pass through anode 3E3, and encounter an' opposing direct current field between anode 'w and a grid 7 3|. Grid'iil is supplied with a'relatively low di-. -rect current potential by potentiometer-3i connected across battery H. The direct current field "between anode 3E! and grid*3l is Of' StlCHStIefigth that many of the electrons that are "slowed down between anode 30 and grid 29 will b'e'turned back, and since the number of electrons turned -back will be dependent on the amplitudeofosciilw :tion in the circuit of which gridsZSantl gfi are a "part, the current flowing from "cylinder -32 through a pair of connected earphones 33' will-be 1 a'function of 'the'amplitude'of oscillation in the circuit of which grids filland 25'are a parti Thus,

theincoming signal is detected.

The detector shown in Fig. ii is' different'frem the'one shown in Fig.2, but it opei'ates' on'the; I same principle, namely that of discriminating :?between electrons according to" the velocity -with which they penetrate the resptztivd pree'dihg It may he here emphasized that this'type of' dete'ction isnot used in'existing" three=e1ec.-. trod'e tube practice; nor is itusable in' s'uch pr-ac- 'tice without special circuit des'ign.

It shou d be mentioned at'thi's point that in all the figures, the electron permeable electrodes have been shown with wire widelyspaced so as to minimize confusion in the drawings. -"'In actual tubes these electrodes would" in general 'contain considerably more grid wires.

1 Fig, 8 illustrates an alternative-arrangementof the device shownin Fig." 6; the onlyldiiference beingthat the control 'grid'fi is nota -part-of a concentriclineresonator as iii' FigJ'B, but receives its alternating current potentialby capacity coupling through annular rings" i'9j-"2fifand 2i =as in Fig. 5, where similar parts bearing the-same'nume- 'b'ers serve the 'samepurposefi Thus it -will-"be apparent that the condenser rings 'of Fig; ES -maybe ''--used in lieu of the concentric lines provided in --Figs'.' 3 and 6. Grid" 28 is conductivel-y connected through resistor 23 to a suitable point on' th'e-bat- -50 =tery. All other parts may bereadily -identifiedby reference to Fig. 6 without furtherexplanation.

' In Fig. 9 an embodiment which operates somewhat similar tothat or Fig 2 isshowng -the principal differences being the"typeof res'o-nator'used and the fact that the control grid'is positively biased in Fig; 9 rather than-negatively biased as "in Fig. 2. 34 is a-heating"filament' which heats a portion of the-12.11 35 of aresonator-structure 36, which wall portion 35 is coated W'ith-an' electron-emitting substance serving as a:c'athode. 3l

isthe control grid which is suitably biased' tc a positive potential through -lead' 'w ane -potentionieter' 38'. -As has been previously explained,

this grid may have a positive bias 'witheut intro- "ducing' a resistiveload 'on theresonant grid- 'cathode circuit. 'Byvirtue'of'thispositive bias, "grids? serves also to accelerate the 'ele'ctrons leaving the cathode 55. 1 Grid is' located in the center of diaphragm 3 9;.Which1rnaYabe momma ous' conducting sheet if it is desired'that t-he space above grid 13] be completely shieldedfroin the space'belcw gridfil, so that resonant oseillations mayexist in both spaces withoutfthe 'os'cillaticns belowgrid 31 reacting on' -the -oscillations above 4 ssgrid 'flfithese spacesctherebycactingsasatwozsepacrate rzcavityiresonators ;:-:for it "may be? perforated 'so as rt'orpermititheinterlinking of :the fiel'dsz'a'hove ridrbelowzthediaphragm", whereb -theitwo"spaces ctzas two: coupled? cavity :resonators. a :fAs inrF-ig. 2 he flightitimeiof'the electrons betweenrca'thode and gr id sfiris arrangedito be a hflfeCYClG'iOl' a ittl'eimore.

ilhiap hra'qni' 39 1is insulated? from the? shells Fof 0 the rcsonators' '40 and" 4 i: xbyl'insulating washers Z and I3i shown fexaggeratediin' thickness; 'ili his 1 allows cathodfi5g'i" grid '31; andtanode M i to else lli operatediatidifierent'directl currentenotentials,

atrthe sam time' allo'wing the alternating cura- -rents in' the walls of the resonator" to flow freely becanse of Ithe relatively high capacity through the insulating material.

Shell dll togethefwith' diaphragnf'w forms a cavity" resonator surrounding' the Fele'ctron "diScharge' -path sbetween' cathode 3'5 and" the rid 37. Similarly,?sl1e l together with 'dia- -phragm B 'deiines a second cavity r'esonator s'urrou'riding t-he F electron path (between g'i'id 3?* andancide M. As is wellkn'own, ultra highirequ'ency currents of the frequencies -uti'liz'e'd in 5 "the 'anod l loff ig'i acts' sirfiilarly to thep'ermeable electrode 5"-"6i'Fig.'2.

'FigI '10 is a cross-sectional view of a modifica- "tionof the device shown iriFig. '6 in which adifferent type of resonator is used for'the resonant 5W3ircuit. 'This'resonator consistsof a closed con- "-"clucting'metalsh'ell which is generated by rotation'of the cross-section shownabout the a'xisof symmetry of T the -cmss section oi the resonator as in Fig. 9. The diaphragm 41, containing ears,

-"-may' betcontinuousyin whichcase closed space 49 :r'is iso'latedt fromcclosed space 58,"and '-these"tW0 osed spaces andtheirconducting-boundariesact .as" twoia'indeperidentrresonatorsf'or suitable apertnres'a'mawbemade in" diaphragm?! so that the =twc Spaces' 'GBIandffifl become coupled'resonators.

. ffllirially; 'finearly'iall whe -diaphragm "may 'be "reni'ove'd so that spaces fi and5'0 become a' 'sin'gle resonator."" 'None"cf these changes willdi'sturb theessential function of the'device.

G0 TI nithe draWinQ-MB lean-indirectly heated cath- 'riode" havin'g a"=circu1aremitting surface facing grid 46. Grid 48 is made positive With=respect to e the cathode so that "electrons are drawn from ithe cathode mid -pass -through grid- 46. *"After passingfgrid 'llfigl' they are slowed *down by "grid 33' whichti's ordinarily slightly negative with re- Tcome tO aistopi just in frcnt'offgridi48,"andreturn 1 to grid llfilfsf rhere isithen'a virtual cathode'iornied at this point in front of grid 'efi. Therelectrons nism whereby energy is supplied to the resonant circuits have already been explained in connection with Fig. 6, this will not be repeated. Grid 48 is insulated from the metal shells of resonators 49 and 50 in the same manner as is the case in the device shown in Fig. 9. Energy may be extracted from resonator 50 by loop 52, conducted over concentric line 53 and radiated from antenna 54. The device of Fig. 10 may also be used as a receiver and amplifier by coupling electromagnetic energy into resonator 49 by means similar to that shown previously in Fig. 6. In this case the current and potential may be adjusted so that the device will either fail to oscillate or will just oscillate. Anode may be made into an electron-permeable electrode, and a detector of the type shown in Fig. 2 or Fig. 6 may be placed behind such electrode.

This structure is shown in Fig. 11 which is the same as Fig. except for the modifications just noted. Thus, in Fig. 11, e ectromagnetic energy is coupled into resonator 49 by line 53 and loop 52, as in Figs. 2 and 9. Also, anode 5|, corresponding to anode 5| of Fig. 10, is made as an electron-permeable grid, and a detector structure of the type of Fig. 6 has been added. comprising grid 5| (equivalent to grid 31 of Fig. 6) and detector plate 62 (equivalent to detector plate 32 of Fig. 6). Detector plate 62 is connected to the positive terminal of battery 25 through receiver 33, as in Fig. 6. Grid BI is connected by lead 63 to a tap on voltage divider 3| connected across battery l1, and is thereby kept at a negative potential, also as in Fig. 6.

The device of Fig. 11 will therefore operate as a receiver and amplifier in the same manner as Fig. 6, with elect ons from cathode 45 being formed in a stream directed toward plate 62. The electrons are periodicall varied in velocity by the alternating field between grids 46 and 48 of resonator 49. Those electrons decelerated by the alternating field are turned back by the negative potential on grid 48, while many of those accelerated will penetrate beyond grid 48 as a density-varied stream to deliver energy to resonator 56. Grid El and plate 62 serve as a detector, the electron current collected by plate 62 flowing through earphones 33 to reproduce the detected incoming signal.

The type of detection made use of in the device described in Fig. 6 may be used at long wave lengths as well as at very short wave lengths, and without the use of concentric line resonators, if desired. The only requirement to obtain this end is that there must not be a difference of alternating current potential between the velocity discriminating grid, as 3| of Fig. 6 and the electron-permeable electrode 30, performing the function of the plate or anode in an ordinary tube, which is the inverse of the alternating current potential difference between the cathode and anode 30.

Since many changes could be made in the above construction and many apparently widely difierent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

. 1. A thermionic device, comprising a resonant hollow conducting member adapted to contain confined electric field oscillations, said member having a reentrant portion spaced from its opposite wall by a distance short compared to the wavelength in free space corresponding to the frequency resonant therein, means aligned with said portion for projecting electrons into said resonant member, and grid means in the interior of said resonant member and insulated therefrom, for causing part of said electrons to be repelled back toward their point of origin, thereby doing work on said field.

2. An electron tube structure comprising a hollow resonator, an emitter adjacent said resonator and outside thereof an accelerating electrode aligned with said emitter for driving electrons from said emitter into said resonator, and means including an electron-permeable repelling electrode within said resonator and insulated therefrom for repelling a portion of said electrons to cause the latter to return toward said emitter and for passing th remainder of said electrons therethrough.

3. High frequency apparatus comprising a cathode, an anode, a control grid, an acelerating grid between said cathode and said control grid, means connected to said acelerating grid for maintaining said accelerating grid at a higher direct potential than said control grid and cathode, a hollow cavity resonator connected between said accelerating grid and said anode, said accelerating grid and said anode constituting portions of the boundary walls of said resonator, said resonator having a resonant frequency such that when oscillations are present in said resonator a part of the electrons passing from the cathode through the accelerating grid will approach the control grid and, due to the lower direct potential of the control grid, will come to rest very close to this control grid in approximately one-half cycle of the frequency of said resonator thereby imparting energy to the circuit, and a part of said electrons will pass on through said control grid, said last-named part of the electrons exciting said resonator.

4. An electron discharge device having a cathode for supplying a stream of electrons, a collector for receiving said electrons, an electrode positioned adjacent the collector electrode, means including a potential source connected .between said cathode and said electrode for positively biasing said electrode a cavity resonator surrounding the discharge path between said cathode and collector for subjecting the electron stream to a high frequency field between said cathode and said positively biased electrode and an output cavity resonator surrounding the electron path between said positively biased electrode and collector.

5. An amplifier including an electron emitting cathode, an electron collector, means for producing an electron stream along a path from the cathode to the collector, a resonant cavity, means comprising a first electrode and a second electrode positioned along the path of the electron stream between the cathode and the collector in the order named and bounding a gap in the resonant cavity for cyclically varying the velocities of the electrons traversing the gap between the electrodes, a second resonant cavity, means comprising the said second electrode and a third electrode, which is positioned along the path of the electron stream between the second electrode and the collector, bounding a gap in the second resonant cavity, the second electrode being common to the two said gaps, whereby density variations in the electron stream traversing the gap in the second resonant cavity may excite electrically that cavity, and means for maintaining the second electrode, which is common to the two gaps, at a direct current potential such that it produces a static retarding field in the gap in the first cavity to turn back electrons which by the cyclic velocity variations have had their velocities reduced while allowing higher velocity electrons to pass on and cross the gap in the second cavity whereby the electron stream traversing the gap in the second cavity is density varied and the second resonant cavity is excited in accordance with the velocity variations impressed upon the electron stream as it traverses the gap in the first resonant cavity.

6. In combination, a pair of hollow electrical resonators in close proximity having substantially a common boundary, aligned apertures in the common and other boundaries of the resonators suitable for projecting an electron stream therethrough, means for projecting an electron stream through the said apertures such that it passes through a portion of the space of one of the resonators and thence through the aperture in the common boundary into a portion of the space of the other resonator, means external to it for energizing at high frequency the said resonator first traversed by the electron stream whereby the velocities of the electrons in the stream are varied at the high frequency and means for producing a retarding field to reduce the velocities of all of the velocity varied electrons and to turn back electrons having had a negative velocity variation permitting only those not turned back to pass through the aperture in the common boundary into the said other resonator thereby exciting it at the said high fre quency.

7. A velocity sorting device for use with an electron beam comprising a resonatin chamber substantially closed against the escape of electromagnetic radiations at the resonant frequency, said resonator comprising two conductive portions insulated from each other, said resonator being coupled with the electron beam and means for impressing a potential difference between the insulated portions of said resonator to produce an electron retarding field between the said insulated portions.

RUSSELL H. VARIAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

